Some combustion engines include a fuel pump assembly having a high pressure fuel pump that delivers fuel under pressure to the engine, and a fuel vapor separator that acts as a fuel reservoir for supplying fuel to the high pressure fuel pump. The fuel pump delivers fuel to a fuel rail and associated fuel injectors. A fuel pressure regulator controls the fuel pressure within the rail and may be mounted on the return or downstream end of the rail with an exhaust or outlet of the fuel pressure regulator communicating with the fuel vapor separator through a fuel return line.
The interior volume of the fuel vapor separator is generally held at a substantially lower pressure than the fuel rail. In addition, the fuel returned to the fuel vapor separator is often heated having been routed near the engine through the fuel rail, and having also been heated by the fuel pump prior to delivery to the fuel rail. Accordingly, fuel vapor is generated when the heated return fuel is discharged into the cooler bulk fuel within the fuel vapor separator. It is desirable to prevent or at least greatly reduce the amount of fuel vapor that is drawn in by the fuel pump and delivered to downstream components to prevent or reduce the possibility of vapor lock, or reduced engine performance and efficiency.
Conventional fuel vapor separators are formed with metal bodies that require extensive machining and subsequent coating or plating to reduce corrosion from both the fuel contained therein and a coolant used to cool the fuel in the separator, which may be water including salt water in some applications. The metal bodies tend to be heavy and expensive to manufacture. Further, conventional fuel vapor separators use a float controlled vent valve assembly to vent vapor from the separator which can become stuck in their closed position and allow higher than desired pressure to build in the vapor separator. Also, water or coolant passages machined in the metal bodies can become plugged with debris in or carried by the coolant and debris resulting from corrosion of the water passage itself.